linux/drivers/spi/spi-bitbang.c
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   1/*
   2 * polling/bitbanging SPI master controller driver utilities
   3 *
   4 * This program is free software; you can redistribute it and/or modify
   5 * it under the terms of the GNU General Public License as published by
   6 * the Free Software Foundation; either version 2 of the License, or
   7 * (at your option) any later version.
   8 *
   9 * This program is distributed in the hope that it will be useful,
  10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 * GNU General Public License for more details.
  13 *
  14 * You should have received a copy of the GNU General Public License
  15 * along with this program; if not, write to the Free Software
  16 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17 */
  18
  19#include <linux/init.h>
  20#include <linux/spinlock.h>
  21#include <linux/workqueue.h>
  22#include <linux/interrupt.h>
  23#include <linux/module.h>
  24#include <linux/delay.h>
  25#include <linux/errno.h>
  26#include <linux/platform_device.h>
  27#include <linux/slab.h>
  28
  29#include <linux/spi/spi.h>
  30#include <linux/spi/spi_bitbang.h>
  31
  32
  33/*----------------------------------------------------------------------*/
  34
  35/*
  36 * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
  37 * Use this for GPIO or shift-register level hardware APIs.
  38 *
  39 * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
  40 * to glue code.  These bitbang setup() and cleanup() routines are always
  41 * used, though maybe they're called from controller-aware code.
  42 *
  43 * chipselect() and friends may use spi_device->controller_data and
  44 * controller registers as appropriate.
  45 *
  46 *
  47 * NOTE:  SPI controller pins can often be used as GPIO pins instead,
  48 * which means you could use a bitbang driver either to get hardware
  49 * working quickly, or testing for differences that aren't speed related.
  50 */
  51
  52struct spi_bitbang_cs {
  53        unsigned        nsecs;  /* (clock cycle time)/2 */
  54        u32             (*txrx_word)(struct spi_device *spi, unsigned nsecs,
  55                                        u32 word, u8 bits);
  56        unsigned        (*txrx_bufs)(struct spi_device *,
  57                                        u32 (*txrx_word)(
  58                                                struct spi_device *spi,
  59                                                unsigned nsecs,
  60                                                u32 word, u8 bits),
  61                                        unsigned, struct spi_transfer *);
  62};
  63
  64static unsigned bitbang_txrx_8(
  65        struct spi_device       *spi,
  66        u32                     (*txrx_word)(struct spi_device *spi,
  67                                        unsigned nsecs,
  68                                        u32 word, u8 bits),
  69        unsigned                ns,
  70        struct spi_transfer     *t
  71) {
  72        unsigned                bits = t->bits_per_word;
  73        unsigned                count = t->len;
  74        const u8                *tx = t->tx_buf;
  75        u8                      *rx = t->rx_buf;
  76
  77        while (likely(count > 0)) {
  78                u8              word = 0;
  79
  80                if (tx)
  81                        word = *tx++;
  82                word = txrx_word(spi, ns, word, bits);
  83                if (rx)
  84                        *rx++ = word;
  85                count -= 1;
  86        }
  87        return t->len - count;
  88}
  89
  90static unsigned bitbang_txrx_16(
  91        struct spi_device       *spi,
  92        u32                     (*txrx_word)(struct spi_device *spi,
  93                                        unsigned nsecs,
  94                                        u32 word, u8 bits),
  95        unsigned                ns,
  96        struct spi_transfer     *t
  97) {
  98        unsigned                bits = t->bits_per_word;
  99        unsigned                count = t->len;
 100        const u16               *tx = t->tx_buf;
 101        u16                     *rx = t->rx_buf;
 102
 103        while (likely(count > 1)) {
 104                u16             word = 0;
 105
 106                if (tx)
 107                        word = *tx++;
 108                word = txrx_word(spi, ns, word, bits);
 109                if (rx)
 110                        *rx++ = word;
 111                count -= 2;
 112        }
 113        return t->len - count;
 114}
 115
 116static unsigned bitbang_txrx_32(
 117        struct spi_device       *spi,
 118        u32                     (*txrx_word)(struct spi_device *spi,
 119                                        unsigned nsecs,
 120                                        u32 word, u8 bits),
 121        unsigned                ns,
 122        struct spi_transfer     *t
 123) {
 124        unsigned                bits = t->bits_per_word;
 125        unsigned                count = t->len;
 126        const u32               *tx = t->tx_buf;
 127        u32                     *rx = t->rx_buf;
 128
 129        while (likely(count > 3)) {
 130                u32             word = 0;
 131
 132                if (tx)
 133                        word = *tx++;
 134                word = txrx_word(spi, ns, word, bits);
 135                if (rx)
 136                        *rx++ = word;
 137                count -= 4;
 138        }
 139        return t->len - count;
 140}
 141
 142int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 143{
 144        struct spi_bitbang_cs   *cs = spi->controller_state;
 145        u8                      bits_per_word;
 146        u32                     hz;
 147
 148        if (t) {
 149                bits_per_word = t->bits_per_word;
 150                hz = t->speed_hz;
 151        } else {
 152                bits_per_word = 0;
 153                hz = 0;
 154        }
 155
 156        /* spi_transfer level calls that work per-word */
 157        if (!bits_per_word)
 158                bits_per_word = spi->bits_per_word;
 159        if (bits_per_word <= 8)
 160                cs->txrx_bufs = bitbang_txrx_8;
 161        else if (bits_per_word <= 16)
 162                cs->txrx_bufs = bitbang_txrx_16;
 163        else if (bits_per_word <= 32)
 164                cs->txrx_bufs = bitbang_txrx_32;
 165        else
 166                return -EINVAL;
 167
 168        /* nsecs = (clock period)/2 */
 169        if (!hz)
 170                hz = spi->max_speed_hz;
 171        if (hz) {
 172                cs->nsecs = (1000000000/2) / hz;
 173                if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
 174                        return -EINVAL;
 175        }
 176
 177        return 0;
 178}
 179EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
 180
 181/**
 182 * spi_bitbang_setup - default setup for per-word I/O loops
 183 */
 184int spi_bitbang_setup(struct spi_device *spi)
 185{
 186        struct spi_bitbang_cs   *cs = spi->controller_state;
 187        struct spi_bitbang      *bitbang;
 188        int                     retval;
 189        unsigned long           flags;
 190
 191        bitbang = spi_master_get_devdata(spi->master);
 192
 193        if (!cs) {
 194                cs = kzalloc(sizeof *cs, GFP_KERNEL);
 195                if (!cs)
 196                        return -ENOMEM;
 197                spi->controller_state = cs;
 198        }
 199
 200        /* per-word shift register access, in hardware or bitbanging */
 201        cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 202        if (!cs->txrx_word)
 203                return -EINVAL;
 204
 205        retval = bitbang->setup_transfer(spi, NULL);
 206        if (retval < 0)
 207                return retval;
 208
 209        dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);
 210
 211        /* NOTE we _need_ to call chipselect() early, ideally with adapter
 212         * setup, unless the hardware defaults cooperate to avoid confusion
 213         * between normal (active low) and inverted chipselects.
 214         */
 215
 216        /* deselect chip (low or high) */
 217        spin_lock_irqsave(&bitbang->lock, flags);
 218        if (!bitbang->busy) {
 219                bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 220                ndelay(cs->nsecs);
 221        }
 222        spin_unlock_irqrestore(&bitbang->lock, flags);
 223
 224        return 0;
 225}
 226EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 227
 228/**
 229 * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 230 */
 231void spi_bitbang_cleanup(struct spi_device *spi)
 232{
 233        kfree(spi->controller_state);
 234}
 235EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 236
 237static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 238{
 239        struct spi_bitbang_cs   *cs = spi->controller_state;
 240        unsigned                nsecs = cs->nsecs;
 241
 242        return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t);
 243}
 244
 245/*----------------------------------------------------------------------*/
 246
 247/*
 248 * SECOND PART ... simple transfer queue runner.
 249 *
 250 * This costs a task context per controller, running the queue by
 251 * performing each transfer in sequence.  Smarter hardware can queue
 252 * several DMA transfers at once, and process several controller queues
 253 * in parallel; this driver doesn't match such hardware very well.
 254 *
 255 * Drivers can provide word-at-a-time i/o primitives, or provide
 256 * transfer-at-a-time ones to leverage dma or fifo hardware.
 257 */
 258
 259static int spi_bitbang_prepare_hardware(struct spi_master *spi)
 260{
 261        struct spi_bitbang      *bitbang;
 262        unsigned long           flags;
 263
 264        bitbang = spi_master_get_devdata(spi);
 265
 266        spin_lock_irqsave(&bitbang->lock, flags);
 267        bitbang->busy = 1;
 268        spin_unlock_irqrestore(&bitbang->lock, flags);
 269
 270        return 0;
 271}
 272
 273static int spi_bitbang_transfer_one(struct spi_master *master,
 274                                    struct spi_message *m)
 275{
 276        struct spi_bitbang      *bitbang;
 277        unsigned                nsecs;
 278        struct spi_transfer     *t = NULL;
 279        unsigned                cs_change;
 280        int                     status;
 281        int                     do_setup = -1;
 282        struct spi_device       *spi = m->spi;
 283
 284        bitbang = spi_master_get_devdata(master);
 285
 286        /* FIXME this is made-up ... the correct value is known to
 287         * word-at-a-time bitbang code, and presumably chipselect()
 288         * should enforce these requirements too?
 289         */
 290        nsecs = 100;
 291
 292        cs_change = 1;
 293        status = 0;
 294
 295        list_for_each_entry (t, &m->transfers, transfer_list) {
 296
 297                /* override speed or wordsize? */
 298                if (t->speed_hz || t->bits_per_word)
 299                        do_setup = 1;
 300
 301                /* init (-1) or override (1) transfer params */
 302                if (do_setup != 0) {
 303                        status = bitbang->setup_transfer(spi, t);
 304                        if (status < 0)
 305                                break;
 306                        if (do_setup == -1)
 307                                do_setup = 0;
 308                }
 309
 310                /* set up default clock polarity, and activate chip;
 311                 * this implicitly updates clock and spi modes as
 312                 * previously recorded for this device via setup().
 313                 * (and also deselects any other chip that might be
 314                 * selected ...)
 315                 */
 316                if (cs_change) {
 317                        bitbang->chipselect(spi, BITBANG_CS_ACTIVE);
 318                        ndelay(nsecs);
 319                }
 320                cs_change = t->cs_change;
 321                if (!t->tx_buf && !t->rx_buf && t->len) {
 322                        status = -EINVAL;
 323                        break;
 324                }
 325
 326                /* transfer data.  the lower level code handles any
 327                 * new dma mappings it needs. our caller always gave
 328                 * us dma-safe buffers.
 329                 */
 330                if (t->len) {
 331                        /* REVISIT dma API still needs a designated
 332                         * DMA_ADDR_INVALID; ~0 might be better.
 333                         */
 334                        if (!m->is_dma_mapped)
 335                                t->rx_dma = t->tx_dma = 0;
 336                        status = bitbang->txrx_bufs(spi, t);
 337                }
 338                if (status > 0)
 339                        m->actual_length += status;
 340                if (status != t->len) {
 341                        /* always report some kind of error */
 342                        if (status >= 0)
 343                                status = -EREMOTEIO;
 344                        break;
 345                }
 346                status = 0;
 347
 348                /* protocol tweaks before next transfer */
 349                if (t->delay_usecs)
 350                        udelay(t->delay_usecs);
 351
 352                if (cs_change && !list_is_last(&t->transfer_list, &m->transfers)) {
 353                        /* sometimes a short mid-message deselect of the chip
 354                         * may be needed to terminate a mode or command
 355                         */
 356                        ndelay(nsecs);
 357                        bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 358                        ndelay(nsecs);
 359                }
 360        }
 361
 362        m->status = status;
 363
 364        /* normally deactivate chipselect ... unless no error and
 365         * cs_change has hinted that the next message will probably
 366         * be for this chip too.
 367         */
 368        if (!(status == 0 && cs_change)) {
 369                ndelay(nsecs);
 370                bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 371                ndelay(nsecs);
 372        }
 373
 374        spi_finalize_current_message(master);
 375
 376        return status;
 377}
 378
 379static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
 380{
 381        struct spi_bitbang      *bitbang;
 382        unsigned long           flags;
 383
 384        bitbang = spi_master_get_devdata(spi);
 385
 386        spin_lock_irqsave(&bitbang->lock, flags);
 387        bitbang->busy = 0;
 388        spin_unlock_irqrestore(&bitbang->lock, flags);
 389
 390        return 0;
 391}
 392
 393/*----------------------------------------------------------------------*/
 394
 395/**
 396 * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 397 * @bitbang: driver handle
 398 *
 399 * Caller should have zero-initialized all parts of the structure, and then
 400 * provided callbacks for chip selection and I/O loops.  If the master has
 401 * a transfer method, its final step should call spi_bitbang_transfer; or,
 402 * that's the default if the transfer routine is not initialized.  It should
 403 * also set up the bus number and number of chipselects.
 404 *
 405 * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 406 * hardware that basically exposes a shift register) or per-spi_transfer
 407 * (which takes better advantage of hardware like fifos or DMA engines).
 408 *
 409 * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
 410 * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
 411 * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 412 * routine isn't initialized.
 413 *
 414 * This routine registers the spi_master, which will process requests in a
 415 * dedicated task, keeping IRQs unblocked most of the time.  To stop
 416 * processing those requests, call spi_bitbang_stop().
 417 */
 418int spi_bitbang_start(struct spi_bitbang *bitbang)
 419{
 420        struct spi_master *master = bitbang->master;
 421
 422        if (!master || !bitbang->chipselect)
 423                return -EINVAL;
 424
 425        spin_lock_init(&bitbang->lock);
 426
 427        if (!master->mode_bits)
 428                master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
 429
 430        if (master->transfer || master->transfer_one_message)
 431                return -EINVAL;
 432
 433        master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
 434        master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
 435        master->transfer_one_message = spi_bitbang_transfer_one;
 436
 437        if (!bitbang->txrx_bufs) {
 438                bitbang->use_dma = 0;
 439                bitbang->txrx_bufs = spi_bitbang_bufs;
 440                if (!master->setup) {
 441                        if (!bitbang->setup_transfer)
 442                                bitbang->setup_transfer =
 443                                         spi_bitbang_setup_transfer;
 444                        master->setup = spi_bitbang_setup;
 445                        master->cleanup = spi_bitbang_cleanup;
 446                }
 447        }
 448
 449        /* driver may get busy before register() returns, especially
 450         * if someone registered boardinfo for devices
 451         */
 452        return spi_register_master(master);
 453}
 454EXPORT_SYMBOL_GPL(spi_bitbang_start);
 455
 456/**
 457 * spi_bitbang_stop - stops the task providing spi communication
 458 */
 459int spi_bitbang_stop(struct spi_bitbang *bitbang)
 460{
 461        spi_unregister_master(bitbang->master);
 462
 463        return 0;
 464}
 465EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 466
 467MODULE_LICENSE("GPL");
 468
 469
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